Dewatering of suspended solids



Sept. 28, 1943- A. J. BARNEBL ET AL DEWATERING OF SUSPENDED SOLIDS FiledDec. 26, 1940 3 Sheets-Sheet 2 SePf- 28, 1943 A. J. BARNEBI. ET Al.2,330,542

DEWATERING 0F SUSPENDED SOLIDS Filed Dec. 26, 1940 5 Sheets-Sheet 5Patented Sept. 28, 1943 DEWATERJNG F SUSPENDED August J. Barnebl,Chicago, Howard D. Grant, Flossmoor, and August C. Barnebl, Chicago,Ill., asslgnors to Swenson Evaporator Company, Harvey, Ill., acorporation of Illinois Application December 26, 1940, Serial No.371,818

(Cl. 21u- 62) 3 Claims.

Our invention relates to the dewatering of suspended solids.

It will be shown and explained as employed to recover sand in a castingcleaning system wherein a high pressure blast of water and wet sand isused to remove adhering molding sand from the castings and todisintegrate cores and remove the core sand.

This application is a continuation in part of our co-pending applicationSerial No. 257,922 filed February 23, 1939.

'I'he principal object of the invention is to provide a process andapparatus which will effectively and economically dewater and dry thesand resulting from the blast, molds and cores so that such as may againbe used for making molds and cores, as distinguished* from that sandwhich may again be diverted to the blast, will be reduced to a so-calledbone dry condition (i. e., containing not in excess of 2% of moisture)which is generally considered to be the best condition for delivery tomolders and core makers, or to those who,` by adding bonding material,prepare the sand for the molders and core makers.

Further to explain the aim of and results obtainable by our invention, abrief explanation of the environment will be helpful. pressure blastcleaning of castings, such for example as set forth in United StatesLetters Patent No. 2,200,587, granted May 14, 1940, is employed, whatmay be termed the waste product resulting therefrom is a water bornemixture or conglomeration made up largely of sand, but also containingnails, wire and other objects used to strengthen cores and molds, scale,clay used as a binder for the foundry sand, fines, coke and other coarsematerials, such as gates and sprues. Various methods may be employed toseparate the useful sand-i. e., proper particle size ranges-from theother solid materials and to clean it and remove the lines, but withsuch steps this invention has nothing to do. For the purpose of ourinvention it can be considered that proper treatment has been employedto provide a magma of water and sand particles of a known sizedistribution suitable for re-use in the making of molds and cores ifonly its moisture content can be reduced to the necessary minimum.

In practice, however, even after such treatment, the magma of water andsand is of a continuously varying concentration. This varyingconcentration is inherent to the blast cleaning because, although theproportions of wet When' a high sand and water of the blast can beregulated to a. nicety and kept substantially constant, the quantitiesof sand removed from castings and derived from core disintegration varyover a wide range. Thus, different castings have different amounts ofsand adhering thereto and require different sizes of cores and, otherthings being equal, the amount of sand removed at the beginning of acleaning operation is, in general, much more than that removed duringthe later stages of cleaning.

Experience demonstrated that this magma of ever varying concentrationcould not be satisfactorily dewatered and dried. No method and meanswere found which could satisfactorily remove the continuously varyingamounts of water in proportion to sand to produce a sand of thenecessary uniformity of dryness. Nor was it found possible continuouslyto remove varying quantities of excess moisture to produce a magma of auniform concentration suitable for effective filtering.

In general, our invention contemplates the reduction of the variableconcentration magma to a magma of a uniform concentration too great foreffective filtering and then the addition of water to transform theuniformly too concentrated magma into a magma of uniformly lessconcentration suitable for effective filtering by what may be termed thebridging method. This method of filtering contemplates the employment ofa filter medium with interstices for the passage of water which arelarger than substantially all-or at least a substantial majority-of thesuspended particles, the escape of an excess quantity of particles beingprevented by their tendency, under proper conditions, to wedge andinterlock into masses or groups which arch or bridge the openings andthereby arrest the movement not only of particles forming the bridges orarches, but also those particles coming behind. And. because of thesomewhat loose or porous character of the deposit thus formed and of thereduction of the liability of particles becoming wedged in theinterstices of the filter medium to blind it, moisture may be eiectivelywithdrawn from the magma.

In the drawings:

Fig. 1 is a somewhat diagrammatic view of equipment for practicing ourinvention in the recovery of mold and core sand:

Fig. 2 is an enlarged longitudinal vertical section through apparatusfor preparing a variable concentration magma of sand and water fornltering and for filtering out and drying the sand;

Fig. 3 is an enlarged partial vertical section at a right angle to thatof Fig. 2, showing more in detail the equipment for concentrating andthen thinning the variable magma and delivering it to the filter;

Fig. 4 is a vertical section on the line'4-L4 of Fig. 2.

Referring iirst to Fig. 1, the broken lines indicate a typical highvelocity water and sand blast casting cleaning system from which aportion of the resultant sand is dewatered and dried in accordance withour invention so that it may be returned to the foundry for re-use bythe molders and core makers. The full lines show a typical embodiment ofthe apparatus for carrying out our invention.

In the utilization of our invention for re-claiming the mold and coresand, the variable concentration magma of water and sand originates atthe casting cleaning location 5 where the castings are freed fromadhering mold sand and cores and the cores are disintegrated by means of.a high pressure stream of water and wet sand projected at high velocityfrom one or more guns 6. The wet sand is supplied to the gun from a sump1 and the high pressure water is supplied to the gun from a suitablesource 8. For further details of such a casting cleaning system,reference may be had to the previously mentioned Patent No. 2,200,587.The floor of the cleaning room may be sloped to a grated drain 9 throughwhich all but the largest of the solid materials removed from thecastings may flow to a screening device i which is designed to removesuch objects as nails, Wire and other solid accessories commonlyemployed to strengthen molds and cores and also sand particles andagglomerates of adhering particles which are larger than desired forre-use in making molds and cores. The good sand, water, fines and othermaterials which flow through the screen are passed to a classified Ilwhere, by the action of upwardly directed Water currents, the morebuoyant fines, clay and soluble materials may be segregated from thegood sand particles and flowed off through a spillway Up to this point,which involves no part of our invention, the resultant magma of goodsand and water, although it has been largely freed from what may begenerally termed impurities, is of a constantly varying concentrationbecause of the very nature of its inception at the cleaning room ashereinbefore explained. It is such a variable concentration magma that,before the advent of our invention, deiied efforts at effective andrapid dewatering and drying to the degree required for ie-use in themaking of molds and cores.

We have found, however, that this variable magma may be satisfactorilytreated for recovery of good sand at the proper dryness by iirstconcentrating the magma to a substantially uniform concentration toogreat for satisfactory filtering, and then by the addition of asubstantially uniform volume of Water, to lower the concentration of theresultant magma to a substantially uniform concentration such as issatisfactory for fiowing to the filter medium and filtering. And we havefound that filtering can be most effectively carried out by arotary-drum type filter in which the interstices through the filtermedium are somewhat larger than substantially allstead of passingthrough the openings in the filtermedium, wedge together and interlockinto masses or groups which arch or bridge across the openings andthereby prevent in large measure the free passage of particles throughthe lter medium. We have found that the deposit or filter cake built upin this manner is suiciently loose or porous to permit effectivedewatering and drying and the filling of the interstices or blinding ofthe filter medium is reduced to a degree such that filtering maycontinuously proceed over long intervals of time.

or at least a substantial majority-of the sus- Now to a detaileddescription of equipment for producing the magma of uniformconcentration su-itable for filtering by the bridging method and forfiltering it by that method.

The variable concentration magma which is too thin is flowed or pumpedfrom the sand classifier Il to a settling tank l of the decanter type.In the decanter there is a gravity concentration of sand at the bottom,which may be and in the practice of our invention is carried to thepoint where .the concentration at the bottom approaches the upper limitof viscous flow and is uniform, and an overflow at the top of excesswater and the less buoyant fines which the classifier has not removed.'I'he magma of this concentration is too viscous either for proper nowto and distribution over the surface of the filter, or for theproduction of the most effective bridging action over or across theinterstices of the lter medium. However, by the addition of water inproper quantity and at a uniform rate to the too concentrated magma inthe region of its emergence from the bottom of the decanter, theconcentration may be lowered and the flow accelerated so that by meansof an elongated chute I6, a magma of substantially constant con--centration may be uniformly fed to and distributed over the surface ofthe drum l1 of the rotary filter IB.

At the filter, which in general maybe of conventional drum type, themagma is dewatered by means of suction provided by a vacuum pump I9acting in the usual manner with a Water trap and through a vacuum line2| connected to the customary distributing chamber of the filter at thetrunnion of the filter drum. Trap 2U may be provided with a barometricleg 22 and a sump 23. Drying of the sand is completed by hot gases whichare produced in a mechanically stoked furnace 24 and forced into thelter housing through a duct 25 by a blower 26.

Referring particularly to Figs. 2 and 3, the equipment for concentratingthe variable magma into a magma of uniform but too great concentrationand for then uniformly thinningit and applying the magma of uniform andproper concentration to the lter drum will now be described.

The settling tank or decanter l5 has a hopper bottom in which-the sandparticles may be settled. The variable magma iiows in from theclassifier Il through an inlet 3l. The sand settles into the hopperbottom 3D and the excess Water, carrying with it only fines and lightersmaller particles. flows over a launder 32 and out through an overiow33. Undue turbulence caused by the inowing magma may be obviated andproper settling of sand particles facilitated by a baiile 34 in thevicinity of inlet 3|. In such a decanter the sand will settle to thebottom of the hopper forming there a magma the concentration of which isuniform and near the upper limit of viscous ow. Its concentration istherefore too great for eective delivery Ito a filter and filtration.

The next step is to dilute this uniformly too concentrated magma by theintroduction of water continuously as the magma -iiows out lof a seriesof spouts 35 projecting from the lower end of the hopper bottom of thedecanter. Dilution to the concentration for proper flow, distributionand bridging action are accomplished by a series of water Jets suppliedthrough a nozzle 38 in each spout 35. Nozzles 36 are connected to a.source 31'of water under pressure and preferably each is equipped withan independent control valve 38. The lower ends of spouts 35 areequipped with suitable reduction connections 39 to each of which isfitted a relatively smallapertured nozzle 40. Because the concentrationof the sand precipitate at the bottom of the decanter I is substantiallyconstant and the water projected through nozzles 36 can be regulated inamount and maintained substantially constant, the concentration of themagma discharged from nozzles 40 can be regulated and maintainedsubstantially uniform. The result is that there can be deposited uponthe sloping floor 4| of the elongated chute I6 a uniformly concentratedmagma of the desired consistency for filtration. The consistency orconcentration and the rate of discharge can be controlled by regulatingthe Water Jets and by changing the bores of the magma discharge nozzles40 which, for this purpose, are preferably made readily removable forsubstitution.

The uniformly concentrated magma flows down the chute I8 onto theperforated surface 42 of the drum l1 of the rotary filter I8 through aslot 43 in the filter housing. 'Ihe direction of drum rotation isindicated by the arrows and a dam 45, tipped if desired with rubberwipers 5B, may be provided to guard against flow of the magma down theperiphery of the drum in the reverse direction. A baiiie 51 may be usedto level down to a uniform thickness the magma as deposited upon thedrums filter surface.

In a foundry producing medium size steel casting, the core and moldingsand recovery has been satisfactorily carried out with a uniformconcentration at the discharge from the settling tank at about BB1/3% ofwater by weight.

The perforated filter surface or filter medium of drum l1 is of metal,having holes-preferably circular-therethrough to provide a mesh withinterstices slightly larger than substantially allor at least asubstantial majority-of the sand particles of the magma flowed thereonfrom chute IB-that is the particles which by screening andclassification have been retained for recovery. At the magma of waterand sand particles, of proper known size distribution and at a uniformconsistency or concentration only slightly above the limit of viscousflow, spreads out uniformly upon the moving surface of the, filtersrotary drum and is subjected to the suction existing upon the interiorof the drum, the particles seeking the places where the suction effectsare most pronouncedi. e., the holes in the filter medium-tend to crowdtogether and approach the holes in groups. Such crowding results inparticles becoming wedged together around and across the holes inbridges or arches which not only prevents particles constituting archesfrom reaching the holes, but sets up a porous barrier against particlesarriving later. 'I'he consequence is that particles do not become wedgedin the interstices of the filter medium,

because they are too small, andneither do they pass through inobjectionable amounts because the bridging or arching eectivelyobstructs most of them. Thus the filter is not clogged or blinded forreasonably long periods of timeperiods long enough for feasiblecommercial operation-and a uniformly porous cake through which thesuction may effectively operate for de watering is accumulated upon thedrums periphery. Therefore, the dewatering starts promptly after themagma is deposited on the drum and progresses rapidly as the caketravels around inside of the 'llter housing. Most of the water iswithdrawn by suction, which has been found to be the least expensivemethod of 'water removal from sand down to something like 7% moisture byweight, and the remainder, sumcient to reduce the moisture content to aslow as 2% by weight, may be removed by evaporation by the blast of hotgases from furnace 24. These gases completely encircle the drum and aresucked through the sand-filter cake upon the drum because of the suctionapplied to the interior of the drum. The outer layers of sand dry fasterthan inner layers and consequently in order progressively to remove theouter dryer layers, a series of Scrapers 60 may be provided. They arearranged so that in the direction of rotation each scraper has itsactive edge closer to the filter medium' surface than does the onebehind. The dried sand removed progressively by the scrapers falls intothe hopper bottom of the filter where it may be fed out through anoutlet chute 62 by a feed screw 63 (drive not shown) which serves toconvey the sand to the outlet where it may be deposited upon a conveyorbelt 64 for return to the molding and core room' or to storage. It isadvisable to locate the conveyor-or it may be a delivery platform-closeenough to the chute 62 to enable the sand flow to accumulate to asuicient extent to block the lower end of the chute suiiiciently toprevent excess air flowing therethrough under the influence of the hotgas blast supplied` to the filter housv ing by blower 26.

Although we have directed our explanation to the treatment of foundrysand, it will be apparent that the invention is applicable to thedewatering and drying of solid particles from varying concentrationmagma of other varieties.

Having thus described the nature and a typical embodimentof ourinvention, what we claim and desire to secure by United States LettersPatent is as follows:

1. The method of dewatering a variable con- A centration magma of waterand insoluble granular solid particles for the recovery of the solids,comprising continuously passing the variable concentration magma to asettling region and there permitting the solids to collect to provide amagma of substantially uniform concentration greater than desired forfiltration and withdrawing excess water continuously from above theconcentrated magma, continuously withdrawing the too highly concentratedmagma from the settling region and adding to such magma water at auniform rate in sufllcient quantity to produce a uniformly concentratedmagma of the concentration desired for filtration, and passing theresultant mixture to a filter.

2. 'I'he method of dewatering a variable concentration magma of liquidand insoluble granular solid particles for the recovery of the solids bymeans of a filter in which the passage of particles through the ltermedium is prevented by bridging action between particles, characterizedby the steps of continuously passing the variable concentrated magma toa settling region, there settling the solids at the bottom to form amagma of substantially uniform concentration greater than that whichwill afford proper ow, withdrawing excess water continuously from abovethe concentrated magma, withdrawing the too concentrated magma from thesettling region and adding thereto Water at a uniform rate and in amountsufcient to pro duce a uniformly concentrated magma of the concentrationwhich will afford proper flow` and bridging action between particles,and passing the resultant mixture to the lter.

3. The method of preparing for filtration to recover the solidstherefrom a varyingly concentrated liquid suspension of granular solidparticles, the lterlng being of the type wherein the passage ofparticles through the lter medium is prevented by bridging action amongparticles, characterized by the steps of continuously passing thevariably concentrated suspension to a settling region and there settlingthe solids to a concentration which is essentially uniform but too highto ow properly to the lter medium and removing excess liquidcontinuously from the settling region, and withdrawing the excessivelyconcentrated mixture from the settling region and adding thereto liquidat a uniform rate and in amount sumcient to produce a. uniformconcentration which will afford proper flow to the lter medium and thereproduce the desired bridging action between particles.

AUGUST J. BARNEBL. HOWARD D. GRANT. AUGUST C. BARNEBL.

